In my previous U.S. Pat. No. 3,706,344, there is set forth a method of completing hydrocarbon producing formations so that optimum conditions prevail during the perforation of the casing. In particular, it has been found desirable for a well casing to be perforated in a manner which provides a minimum of back pressure against the newly perforated formation, so that the formation pressure differential is utilized to its fullest extent in order to expel any foreign material therefrom, thereby avoiding contamination of the sensitive formation. Moreover, when the formation is allowed to expend all of its energy towards the initial flow, the perforations are cleaned and enlarged to the maximum attainable value which can ever be achieved during the life of the borehole.
In my previous U.S. Pat. Nos. 3,706,344 and 4,009,757, there is set forth a perforating gun having a gun firing head thereon which is responsive to impact. In my U.S. Pat. Nos. 3,871,448 and 3,931,855, there is set forth a vent assembly which is opened in response to the setting of a packer.
The combination of either of the first two recited patents with either of the second recited two patents enable a formation to be completed in the above recited desired manner. However, in carrying out this well completion task, it is necessary to have equipment on hand which enables manipulation of the packer by movement of the tubing string. Equipment of this type is expensive.
It would therefore be desirable to be able to set a packer, and to leave a casing gun downhole in an isolated condition until some subsequent time when it is more convenient to complete the well. It would also be desirable if the well could be completed by opening a vent string and immediately thereafter perforating the hydrocarbon containing formation. Apparatus and method for achieving these desirable and unique goals is the subject of the present invention.